This disclosure relates generally to the field of golf clubs. More particularly, it relates to a golf club head with a textured striking face for imparting greater spin to a golf ball when the golf ball is struck.
A common goal of golf club head design, specifically for iron-type and utility-type club heads, and particularly for wedges, is to create a striking face for the club head that imparts significant spin to a struck ball. The striking face of such a club head typically has a plurality of parallel horizontal grooves or score lines. These score lines assist in imparting spin at least by channeling water and debris, and by increasing the friction between the striking face and the surface of the ball. The spin-imparting qualities provided by such score lines are limited, however, by United States Golf Association (“USGA” herein) regulations governing score line geometry (and similar regulations of other international golf equipment regulatory bodies). Moreover, conventional score lines fail to account for low-scale dynamic interactions between the striking face and the ball.
Further improvements in the spin-imparting characteristics of club head striking faces have included the provision of low-scale surface textures in addition to, or in place of the conventional score lines. Such surface textures, however, tend not to take into account the specific interaction between a conventional elastomer-covered golf ball and a metallic striking face. Moreover, conventional surface texturing is subject to rapid wear, is often costly to produce, and may detract from the aesthetic quality of the club head. Furthermore, conventional striking face textures are generally ineffective at providing a high degree of spin for each of the multitude of different types of golf shots that a golfer may attempt. For example, a ball hit with a club having a conventional club head that is swung at a specific speed would have different degrees of spin depending on whether the ball is squarely addressed by the club face or hit with an open club face. Other conditions, such as moisture on the club face and/or the ball, and whether the ball is struck with a full swing, half swing, or chip-type swing of the club, can affect the degree of spin imparted to the ball.
The creation of spin, particularly back-spin, on a struck golf ball, is largely a function of the magnitude of the frictional contact or “traction” between the striking face of the club head and the ball on impact. Where a high degree of back-spin is desired, as in higher number irons and wedges, maximizing this traction factor is therefore a design goal. Increased traction is generally associated with increased surface roughness of the striking face. Surface roughness is commonly expressed in terms of Ra, defined as follows:
      R    a    =            1      n        ⁢                  ∑                  i          =          1                n            ⁢                          ⁢                                y          i                            
where n is the number of sampling points and y is the deviation from a mean line (at a given sampling point). As a practical matter, Ra represents the average of deviations from a mean line over a 2-dimensional sample length of a surface.
Another surface roughness parameter is known as Rt (sometimes referred to as Ry). This parameter represents the maximum peak-to-trough distance in a given 2-dimensional sample length of a surface.
The regulations of the USGA limit the surface roughness of the striking face of golf clubs generally to a degree of roughness no greater than that imparted by sand-blasting or fine milling. In practical terms, this standard has been interpreted to mean a surface having a value of Ra no greater than 0.0046 mm (180 μin.), and a value of Rt of no more than 0.025 mm (1000 μin.). Thus, the need is evident to maximize the traction between the club face and the struck ball without exceeding the roughness maximum established by USGA rules.
Accordingly, a textured striking face for a golf club head has been sought that imparts a high degree of spin to the ball for a wide variety of golf shots under a wide variety of conditions, that has good wear characteristics, that complies with USGA rules, and that enhances (or at least does not detract from) the aesthetic qualities of the club head.